The present invention relates generally to negative pressure air bearing sliders for use in a disk drive, and more particularly to a negative pressure slider having one or more trailing edge pockets in combination with one or more optimized leading edge pockets for a flat fly height profile.
Conventional "positive" air bearing sliders ride on a cushion of air generated by the rotation of a magnetic disk. The upward force on the slider provided by the air cushion is directly proportional to rotational velocity, and hence varies from the inner disk diameter (ID), to the outer disk diameter (OD). Since air bearing sliders tend to be sensitive to such changes in upward force, their fly height will vary across the disk. A plot showing the variation in a slider's flying height from the ID to OD represents the "fly height profile" of that slider. It is generally desirable to optimize a slider to provide a flat fly height profile.
Typically, a positive air bearing slider displays an increase in fly height with increasing velocity. To obtain a more constant fly height profile, some slider designs include a trailing edge negative pressure "pocket". The pocket is generally formed by providing a cross-bar between the "catamaran" rails of a slider, thereby forming a U-shaped air bearing surface (ABS) opening out to the slider's trailing edge. A slider having a negative pressure pocket is referred to in the art as a negative pressure air bearing slider. An example of one such negative pressure air bearing slider is disclosed in U.S. Pat. No. 4,475,135.
Although U-shaped negative pressure air bearing sliders are an improvement over positive pressure designs, their fly height profiles still tend to increase with increasing velocity. This tendency is due to the fact that the negative pressure generated by the pocket cannot fully compensate for the positive pressure of the catamaran rails. To counteract this problem, some negative pressure sliders include a second U-shaped pocket opening out to the leading edge of the slider. This type of negative pressure slider has a generally H-shaped ABS. The leading edge pocket channels more air over the cross-bar, thereby generating greater negative pressure in the trailing edge pocket to improve its efficiency. An example of one such negative pressure slider is disclosed in U.S. Pat. No. 3,855,625.
One problem associated with H-shaped designs, however, is overcompensation resulting from the generation of too much negative pressure. A leading edge pocket having the same width as the trailing edge pocket generally has a linear fly height profile showing decreasing fly height from ID to OD. One solution has been to vary the etch depth of the trailing edge pocket to even out the profile. This design requires a more complex manufacturing process than a slider with pockets at the same etch depth. Another alternative has been to recess the cross bar between the catamaran rails. The recessed cross bar permits air flow from the leading edge pocket to vent into the trailing edge pocket, thereby decreasing the efficiency of the latter. A slider having a recessed cross-rail is disclosed in U.S. Pat. No. 4,218,715. But this alternative also requires a more complicated manufacturing process. What is needed is a method for optimizing the leading and trailing edges pockets of a negative pressure slider having substantially the same etch depth.
As an additional consideration, the negative pressure air bearing sliders described above produce large negative loads, and hence have high stiffness. Consequently, disk degradation due to slider impact with asperities is increased. A number of alternative negative pressure air bearing sliders optimize the amount of negative pressure while retaining the benefits of negative pressure designs. Optimization mechanisms include reduction in pocket size, positioning of the pocket, and distribution of the negative load between two or more pockets. U.S. Pat. No. 5,438,467 discloses such optimized designs and is incorporated herein by reference. What is needed, for a given trailing edge pocket slider design and in a disk drive having given inner and outer diameter fly height tolerences, is a method for determining a leading edge pocket design optimized to provide a desired slider fly height profile.